The effect of Giardia lamblia trophozoites on lipolysis in vitro

Giardia Alters Commensal Microbial Diversity throughout the Murine Gut

Giardia lamblia is the most frequently identified protozoan cause of intestinal infection. Over 200 million people are estimated to have acute or chronic giardiasis, with infection rates approaching 90% in areas where Giardia is endemic. Despite its significance in global health, the mechanisms of pathogenesis associated with giardiasis remain unclear, as the parasite neither produces a known toxin nor induces a robust inflammatory response. Giardia colonization and proliferation in the small intestine of the host may, however, disrupt the ecological homeostasis of gastrointestinal commensal microbes and contribute to diarrheal disease associated with giardiasis. To evaluate the impact of Giardia infection on the host microbiota, we used culture-independent methods to quantify shifts in the diversity of commensal microbes throughout the gastrointestinal tract in mice infected with Giardia We discovered that Giardia's colonization of the small intestine causes a systemic dysbiosis of aerobic and anaerobic commensal bacteria. Specifically, Giardia colonization is typified by both expansions in aerobic Proteobacteria and decreases in anaerobic Firmicutes and Melainabacteria in the murine foregut and hindgut. Based on these shifts, we created a quantitative index of murine Giardia-induced microbial dysbiosis. This index increased at all gut regions during the duration of infection, including both the proximal small intestine and the colon. Giardiasis could be an ecological disease, and the observed dysbiosis may be mediated directly via the parasite's unique anaerobic fermentative metabolism or indirectly via parasite induction of gut inflammation. This systemic alteration of murine gut commensal diversity may be the cause or the consequence of inflammatory and metabolic changes throughout the gut. Shifts in the commensal microbiota may explain observed variations in giardiasis between hosts with respect to host pathology, degree of parasite colonization, infection initiation, and eventual clearance.

The significance of Sarcina in routine surgical pathology practice

Sarcina was first described by Goodsir. The appearance of this bacterium is so characteristic that the diagnosis can be made on light microscopy. Although the original description of Sarcina was made more than 150 years ago, little is known about its role in various human diseases. This study was undertaken with the aim to analyze critically the reason for this sudden recent interest in human Sarcina infection. The results indicate that Sarcina is a histopathological marker of functional or anatomical causes of gastric stasis, and has a possible association with life-threatening emphysematous gastritis. Hence, its documentation in the final report is warranted as the patient might need further work-up.

Probiotic Lactobacillus rhamnosus GG modulates the mucosal immune response in Giardia intestinalis-infected BALB/c mice

BACKGROUND

Gut homeostasis can be altered by the oral administration of health-promoting microorganisms, namely probiotics that are known to reinforce the host immune response.

AIM

The aim of this study was to elucidate the immunomodulatory effect of orally administered probiotic Lactobacillus rhamnosus GG (LGG) in Giardia-infected mice.

METHODS

BALB/c mice were fed orally with probiotic LGG either 7 days prior to or simultaneously with the challenge dose of Giardia trophozoites. The administration of the probiotic was continued for 25 days, and immunomodulatory potentials in terms of secretory immunoglobulin A (IgA) levels, CD8+ and CD4+ T lymphocytes, and expression of pro-inflammatory [tumor necrosis factor-alpha, interferon-gamma (INF-γ)] and anti-inflammatory cytokines [interleukin (IL)-4, IL-6, IL-10] were studied.

RESULTS

Oral feeding of LGG prior to or simultaneously with the test dose of Giardia seems to have modulated both arms (humoral and cellular) of the mucosal immune system since a significant increase in the levels of specific secretory IgA antibody, IgA+ cells, and CD4+ T lymphocytes were observed in contrast with the decreased percentage of cytotoxic CD8+ T lymphocytes. The stimulated mucosal immune response in probiotic fed Giardia-infected mice was further correlated with the enhanced levels of anti-inflammatory cytokines IL-6 and IL-10 and reduced levels of pro-inflammatory cytokine INF-γ.

CONCLUSIONS

This is the first study to show that oral administration of the effective probiotic LGG to Giardia infected mice could be used as a bacterio-therapy that restores the normal gut microflora and modulates the mucosal immune response.

Protozoan infections of the gastrointestinal tract

The review provides current views on human protozoan parasites of the gut. The recognition of the importance of cryptosporidium, cyclospora and microsporidia over the last three decades emphasises the possibility that more pathogenic intestinal protozoa are presently unrecognized. Each of these is a zoonotic infection and the potential for a zoonotic element to the transmission of giardiasis has been recognized. A common theme in increased understanding of the biology and pathological mechanisms involved in causing disease is the application of molecular techniques to the various stages of the parasite life cycle. Molecular methods are increasingly contributing to laboratory diagnosis of these conditions with increased yields of positive results though in the tropics it is likely that fecal microscopy will remain the standard for some time to come. The nitroimidazole compounds are the mainstay of treatment for giardia and amebiasis with no major advance in therapeutics since their role was appreciated. Nitazoxanide was shown to be effective for cryptosporidiosis in the 1990s.

Microarray analysis of the intestinal host response in Giardia duodenalis assemblage E infected calves

Despite Giardia duodenalis being one of the most commonly found intestinal pathogens in humans and animals, little is known about the host-parasite interactions in its natural hosts. Therefore, the objective of this study was to investigate the intestinal response in calves following a G. duodenalis infection, using a bovine high-density oligo microarray to analyze global gene expression in the small intestine. The resulting microarray data suggested a decrease in inflammation, immune response, and immune cell migration in infected animals. These findings were examined in more detail by histological analyses combined with quantitative real-time PCR on a panel of cytokines. The transcription levels of IL-6, IL-8, IL-13, IL-17, and IFN-γ showed a trend of being downregulated in the jejunum of infected animals compared to the negative controls,.No immune cell recruitment could be seen after infection, and no intestinal pathologies, such as villus shortening or increased levels of apoptosis. Possible regulators of this intestinal response are the nuclear peroxisome proliferator-activated receptors alpha (PPARα), and gamma (PPARγ) and the enzyme adenosine deaminase (ADA), all for which an upregulated expression was found in the microarray and qRT-PCR analyses.

Intestinal infection with Giardia spp. reduces epithelial barrier function in a myosin light chain kinase-dependent fashion

BACKGROUND & AIMS

Giardiasis causes malabsorptive diarrhea, and symptoms can be present in the absence of any significant morphologic injury to the intestinal mucosa. The effects of giardiasis on epithelial permeability in vivo remain unknown, and the role of T cells and myosin light chain kinase (MLCK) in altered intestinal barrier function is unclear. This study was conducted to determine whether Giardia spp. alters intestinal permeability in vivo, to assess whether these abnormalities are dependent on T cells, and to assess the role of MLCK in altered epithelial barrier function.

METHODS

Immunocompetent and isogenic athymic mice were inoculated with axenic Giardia muris trophozoites or sterile vehicle (control), then assessed for trophozoite colonization and gastrointestinal permeability. Mechanistic studies using nontransformed human duodenal epithelial monolayers (SCBN) determined the effects of Giardia on myosin light chain (MLC) phosphorylation, transepithelial fluorescein isothiocyanate-dextran fluxes, cytoskeletal F-actin, tight junctional zonula occludens-1 (ZO-1), and MLCK.

RESULTS

Giardia infection caused a significant increase in small intestinal, but not gastric or colonic, permeability that correlated with trophozoite colonization in both immunocompetent and athymic mice. In vitro, Giardia increased permeability and phosphorylation of MLC and reorganized F-actin and ZO-1. These alterations were abolished with an MLCK inhibitor.

CONCLUSIONS

Disruption of small intestinal barrier function is T cell independent, disappears on parasite clearance, and correlates with reorganization of cytoskeletal F-actin and tight junctional ZO-1 in an MLCK-dependent fashion.

Giardiasis

Despite rapid progress in understanding the biology of Giardia, several questions remain unanswered. First, there is no adequate explanation for the diverse clinical spectrum of giardiasis. Second, the mechanisms by which Giardia produces diarrhea and malabsorption are poorly understood, although some progress has been made. Finally, despite extensive studies in animal models and human infections, the key immunologic determinants for clearance of acute infection and development of protective immunity remain ill defined. This article discusses the epidemiology, pathology, diagnosis, treatment, and prevention of giardiasis.

Intestinal lipid metabolism in suckling rats infected with Giardia duodenalis

We carried out a quantitative and qualitative analysis of intestinal digestion of neutral lipids in suckling rats infected with Giardia duodenalis. Total lipids were measured after extraction from the contents of the stomach, proximal and distal small bowel, caecum and colon. Amounts gradually fell from the stomach to the colon and were identical in infected animals and controls, although high values were occasionally found in the caecum of infected rats. Relative glyceride quantities were determined by means of high-performance thin-layer chromatography. Triglycerides were absent from the distal small bowel, and only free fatty acids and cholesterol were present in the caecum, reflecting normal digestion of neutral lipids in infected suckling rats. Our results suggest that G. duodenalis does not impair intestinal fat digestion in suckling rats.

Diarrhoeal disease: current concepts and future challenges. Pathogenesis of giardiasis

Giardiasis is the most common small intestinal protozoal infection and is found worldwide. The mechanisms by which Giardia duodenalis (= G. lamblia) produces chronic diarrhoea and malabsorption have still not been clearly defined. Many infections are associated with mild to moderate mucosal damage which, in animal models of infection, have functional correlates. Possible mechanisms include direct physical injury, release of parasite products such as proteinases or lectin, and mucosal inflammation associated with T cell activation and cytokine release. Other possible mechanisms of malabsorption include associated bacterial overgrowth and bile salt deconjugation, bile salt uptake by the parasite with depletion of intraluminal bile salts, and inhibition of pancreatic hydrolytic enzymes. Thus, there is no single mechanism to explain the diarrhoea and malabsorption caused by Giardia, which currently should be regarded as a multifactorial process.

Secretin-cerulein test and fecal chymotrypsin concentration in children with intestinal giardiasis

We studied six patients with giardiasis (five males, one female), median age 3.5 yr (range 1-11) and 12 healthy control subjects (10 males, 2 females), median age 3.5 yr (range 1-10). Intestinal biopsy and a contemporaneous secretin-cerulein test were performed in all patients, and fecal chymotrypsin was also assayed. Intestinal biopsy was normal in five of the six patients with giardiasis, whereas one of the six presented a partial atrophy of the intestinal villi. The secretin-cerulein test (1 CU/kg of secretin + 75 ng/kg of cerulein) did not show any significant difference between values in the outputs of chymotrypsin, lipase, phospholipase, and bicarbonate obtained in patients and in controls; however, in the one patient with partial intestinal mucosal atrophy, all enzymatic activity levels were below the normal limit for our laboratory. Furthermore, the mean values of fecal chymotrypsin concentration did not differ between the two groups. Fecal chymotrypsin was also reduced in the patient with an abnormal secretin-cerulein test; a second assay performed 3 mo after the suspension of treatment (Metronidazole), however, showed a normal chymotrypsin concentration.

The effect of Giardia lamblia trophozoites on trypsin, chymotrypsin and amylase in vitro

Giardia lamblia localize and multiply in the small intestine and may cause acute or chronic diarrhoea with malabsorption of fat, protein and other nutrients. Abnormal pancreatic function has been documented in giardiasis and trophozoites directly inhibit pancreatic lipase activity in vitro. The aim of this study was to examine the effect of Giardia trophozoites on pancreatic trypsin, chymotrypsin and amylase activity in vitro. Axenically cultured Giardia trophozoites (Portland-1 stock) were incubated with a range of concentrations of trypsin, chymotrypsin and amylase and enzyme activity assayed over time. Tryptic activity was decreased after incubation with Giardia trophozoites. This reduction was time dependent and linear over the incubation period of 2 h. At a trypsin concentration of 18 BAEE units/ml, there was a 35.5 +/- 4% reduction in enzyme activity after 2 h compared to controls. The total amount of activity lost was proportional to the initial trypsin concentration up to 185 BAEE units/ml. At this initial concentration, the activity was reduced by 46.5 +/- 3 units/ml after 2 h. Above this concentration, little further loss of enzyme activity was seen. To investigate the nature and specificity of this effect, similar experiments were conducted using killed trophozoites and with a related protozoan, Trichomonas vaginalis. No loss of enzyme activity was evident. Media previously incubated for 2 h with trophozoites did not diminish tryptic activity. Trophozoites had no effect on chymotrypsin or amylase activities over the range of concentrations tested.(ABSTRACT TRUNCATED AT 250 WORDS)